Electronic systems generally include at least one printed wiring board (PWB) containing one or more integrated circuit (IC) chips or ICs. The IC may be packaged in a number of conventional ways. One prevalent IC package is known as a ball grid array (BGA) package. The name comes from the array of solder balls that are formed on the bottom of the package. The PWB has a corresponding array of pads to which the solder is bonded during the affixing of the BGA package to the PWB. The resulting interconnection is capable of serving a wide variety of applications.
Turning first to FIG. 1, a schematic diagram of two views of a conventional BGA package to PWB interconnection system 10 is shown. The schematic is not to scale. The upper view is a plan view and the lower view is an elevation view. The system 10 includes a BGA package 12 and a PWB 14. The BGA package 12 includes a chip 16, a package substrate 18, and an array of a plurality of solder balls 19. The size, shape, type, and location of the chip 16 will depend on the circumstances but is generally centered on the package substrate 18. The size and shape of the package substrate 18 will depend on the circumstances but is generally rectangular and often square as shown. The size, number, and arrangement of the plurality of solder balls in the array 19 will depend on the circumstances but is generally formed of solder balls of uniform size in rectilinear rows and columns having uniform spacing or pitch in both directions.
In the electronics industry, improvements in functionality and performance are driving the demands for integration to unprecedented levels. With respect to the BGA package 12, the conventional response to the demands has been to increase the size of the package substrate 18, to shrink the pitch of the array 19, or both. These responses increase the number of contacts. Eventually a practical limit will be reached and a new approach will be desired. This is especially true given that higher current demands posed by the higher integration are eroding the relative contact gains of the conventional approach, that is, more and more of the new contacts are dedicated to power delivery and ground connections and not to signal communication.